Verification of positioning accuracy of MLC leaves of 7 medical electronic linear accelerators in IMRT in Sichuan province / 中华放射医学与防护杂志

ABSTRACT

Objective To verify the accuracy of multi-leave collimators (MLC) leaves position in intensity modulated radiation therapy (IMRT) using radiochromic films.Methods 7 medical electronic linear accelerators of Varian,Elekta or Siemens design were chosen.25 cm× 25 cm films were put on 30 cm×30 cm×3.0 cm homogeneous solid phantom and covered with a 2.0 cm thick of homogeneous solid phantom.The CT scanned images were transmitted to TPS for plan preparation.A 5 strip picket fence pattern was formed by MLC leaf,each 3 cm long and 0.6 cm wide,with 3.0 cm wide strip separation.At the maximum dose point,the SSD was 100 cm,with 250 MU per strip.After exposure,the films were transmitted to the dosimetry laboratory at IAEA for measurement and calculation.Results For 6 of 7 accelerators chosen,the differences of film-measured and TPS-planned MLC leaf position for every fence were within ± 0.5 mm as required by IAEA,and the other one not consistent with the requirements.The difference of film-measured MLC leaf position between each pair and all pair for 7 accelerators were within ± 0.5 mm,in line with IAEA's requirements.The differences of film-measured MLC leaf actual width were within 0.75 mm,as required by IAEA,for 6 accelerators and-0.8 mm for the other one,not consistent with the IAEA requirements.The standard deviations of film-measured MLC leaf actual width for all pairs for 6 accelerators were ＜0.3 mm,in line with IAEA requirements,but 0.4 mm for the other one,not consistent with IAEA requirements.Conclusions It is simple,fast and accurate to use radiochromic films for verification of the accuracy of MLC leaf position in IMRT.Therefore it is advisable to widely use radiochromic films in IMRT clinical practice.